INTERFEROMETER

Albert Abraham Michelson Michelson Interferometer Albert Abraham Michelson (1852-1931)

Experimental set up

In Michelson interferometer Radius of nth dark ring

Haidinger Fringe

Order of the fringe Angular radius of the pth ring Formation of both real and virtual fringes

Fringe collapse/emergence

1. Measurement of wavelength of light

2. Measurement of wavelength separation of a doublet

Concordance

Discordance = (q+1/2)

Measurement of the coherence length of a spectral line Formation of straight white light fringes Measurement of thickness of thin transparent flakes Measurement of refractive index of gases Standardization meter

Localization of Newton-Michelson rings

L = a R / U d = 2a – 2U /(R – 2U) Michelson interferometer: R L Newton’s rings: a 0 L 0

Newton’s Ring U<<R & U>>d

Optical Coherence Tomography

Problem The irradiance seen on the top surface of the wings of a Morpho butterfly is due to the constructive interference of the light reflected by thin terraces of transparent cuticle-like material. The terraces extend outward, parallel to the wing. The electron micrograph of the cross-section of the central structure of the terrace is shown in (a) next slide. The terraces have index of refraction n=1.53 and thickness Dt=63.5 nm; and they are separated (by air) by Da=127 nm [see fig (b)]. The visible light falls nearly normally on the terraces (in Fig. b the incident angle is exaggerated for the understanding of the problem). Show that the interference produced by r1 and r3 will produce the visible color. What is the major color from the wing of the Morpho butterfly?

Problem In an experiment with MI, the successive readings for maximum distinctness were found to be 0.6939 mm and 0.9884 mm displacement of M2. If the average wavelength for the two components of D lines be 5893 Å, deduce the difference in wavelength.